Shulou(Shulou.com)11/24 Report--

"falling red is not a heartless thing, it turns into spring mud to protect flowers." when petals and leaves come to the end of life, they fall to the ground with the wind, year after year. However, with the passage of time for thousands of years, layers of fallen leaves did not appear as expected, and layers of fallen leaves disappeared quietly.

This may be the role of fallen leaves that we are most familiar with, which are scattered into mud, turned into fertilizer, absorbed by the roots of plants, and silently nourish their growth, that is, what we often call fallen leaves returning to their roots. The essence of this process is the decomposition of litter. First of all, the animals in the soil (such as earthworms, ants, etc.) will make the dead branches and leaves into fragments, and then the soil microorganisms will further decompose these fragments into simple inorganic molecules or convert them into humus.

However, just like human beings, decomposers are not "open to everything". There will always be things they don't like or can't eat, and they will say no to some roots, stems and leaves. Then, these remnants are gradually covered and buried in the soil, and when we pluck away the soil and look at the plant remains that existed in the sediments thousands of years ago or more, they seem to travel through time and space to tell us that falling leaves are not just returning to their roots.

What is a plant residue? Plant residues are the residues of dead plants that have not been decomposed by microorganisms, and the roots, stems and leaves of plants are generally the most common.

Under natural vegetation, plant residues are mainly leaves, branches, flowers and fruits, dead roots of woody plant litter and dead roots of herbaceous plants.

In the cultivated soil, it is mainly the fallen flowers and leaves of crops, as well as the stubble and part of the straw left after harvest.

In the lake ecosystem, a large number of aquatic plants die in autumn and winter, and most of the plant residues will be deposited in the surface sediments, including incomplete decaying aquatic plant stems, leaves, fibrous fragments, seeds and so on. It is deposited year after year in the form of remnants under the environment of hypoxia at the bottom of the lake, which is an important part of the biological deposition on the lake floor.

Application of plant residues in lake sediments (Wang Yuhui et al., 2017) Plant residues in lake ecosystems at present, the research on plant residues is mainly focused on the decay of straw in agricultural arable land, but the study of plant residues in lake sedimentation has been paid more and more attention. Related studies can be used to explore the paleoenvironmental evolution of lakes and reveal the eutrophication process of lakes. The environmental assessment of urban lakes is carried out to a certain extent, so as to provide some reference and scientific basis for the management and pollution prevention policy of urban lakes in our country.

1. Response to the environment (eutrophication, paleoclimate) by comparing the element distribution patterns of sediments and plant residues at different sedimentary depths, the researchers found that the element concentrations in plant residues changed regularly with depths, while the element concentrations in sediments fluctuated little with sediment depth, indicating that, in contrast, the element assemblage characteristics of plant residues were more sensitive to environmental changes. Aquatic plant residues can also be used as evidence materials for the study of lake sedimentology. The analysis of its TP (total phosphorus) content and its vertical distribution can trace the change process of lake environment and nutrients.

2. Isotopes in plant residues with the deepening of paleoclimate research, scholars hope to more accurately understand the specific process and change mechanism of some important climate events, in addition to high-resolution samples, high-precision age results are also particularly important. 14C dating is one of the main methods for high precision dating of lake sediments. The sample age can be calculated according to the decay degree of 14C, but the 14C dating results of different dating materials will have different errors, which will affect the interpretation of climate indicators.

Compared with the whole sample organic matter, the use of plant residue dating can avoid the effect of carbon pool to a certain extent. It is generally believed that leaves and seeds are mostly annual organic components, so the 14C age of primary deposited leaves and seeds can best represent the formation age of sediments. On the other hand, there is a "penetration time" effect in bark, branch and trunk, especially the "penetration time" of tree root or grass root is more serious, which needs to be carefully selected in 14C dating.

In addition, carbon and oxygen isotopes of plant residues also play an important role in paleoclimate research. Some scholars have used the terrestrial C3 plant residue δ 13C of the Kanas Lake core to explore the response of regional temperature to global climate change in the past 600 years. The climate warming recorded by the δ 13C sequence is consistent with the temperature records of ice core, lake sediment and tree ring reconstruction, indicating that the δ 13C sequence of plant residues can also reflect the climate information very well. In addition, the cellulose oxygen isotope δ 18Ocellulose of peat plant residues is also considered to be one of the important means to study paleoclimate change, and can be used as a substitute index for large-scale water vapor cycle transformation. For example, Alaskan peat δ 18O has successfully reconstructed the intensity change of Aleutian low pressure since Holocene.

Age framework of core FJ19A and distribution of organic matter components in Jiulongchi, Fanjingshan, Guizhou (Rong Yttrium Manganese et al., 2022)

Rong Yttrium Manganese, Peng Haijun, Ding Hanwei, etc. Study on ^ (14) C chronology and Holocene carbon accumulation rate of sediments from Jiulong Pond, Fanjing Mountain, Guizhou Province [J]. Earth and Environment, 2022 (001): 050.

Yang Mingsheng, Huang Xiaoxiang, Wang Dianbei, et al. Distribution characteristics of nitrogen and phosphorus in sediments and aquatic plant residues of wild boar lake in Xiaogan city [J]. Journal of Hubei Institute of Engineering, 2019, 39 (6): 5.

Wang Yuhui, Huang Xiaozhong, Peng Wei, et al. Temperature fluctuation recorded by carbon isotopes of plant residues in Kanas Lake [J]. Science Bulletin, 2017, 62 (24): 11.

Li Shihong, Li Xiaomei, Mao Xueying, et al. INAA study on biogeochemical characteristics of sediments and plant residues in West Lake, Fildes Peninsula, Antarctica [J]. Nuclear Technology, 2005, 28 (4): 6.

[5] Jones M C, Wooller M, Peteet D M. A deglacial and Holocene record of climate variability in south-central Alaska from stable oxygen isotopes and plant macrofossils in peat [J]. Quaternary Science Reviews, 2014, 87: 1-11.

This article comes from the official account of Wechat: stone popular Science Studio (ID:Dr__Stone), author: Zhixing

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